This invention relates to the field of time-interval measurement, and more particularly to the field of displaying time-interval measurement results as a voltage on an oscilloscope as they occur and without interruption.
In the design, debugging, maintenance or repair of electronic circuits, it is frequently desirable to be able to measure time-intervals. From monitoring pulse code modulation behavior to time base stability measurements to analyzing various sorts of time varying behaviors of signals, the need to effectively analyze the time-intervals of electronic signals, especially digital signals, is a major, long felt need in the electronics industry. Until now, effective tools for this type of measurement have been limited, complicated, expensive or difficult to use.
Attempting to make these measurements with a conventional oscilloscope meets with limited success, especially for signals whose time varying behavior interferes with the triggering process. Digital storage oscilloscopes do allow for after-the-fact analysis of stored records by either an operator or post-processing software. But record length is limited, real-time analysis is impossible, and so is continuous analysis beyond the record length. Similarly, high speed logic analyzers can acquire, store and analyze later information about the timing behavior of digital signals, but with the same type of limitations.
Another approach has been emerging in recent years. Variously called time-interval analyzers, modulation domain analyzers, or digital timing analyzers, these instruments analyze time-interval information and display the results as a graph of frequency versus time, time-interval versus time, or time-interval versus number of occurrences.
Some of these instruments rely on sampling techniques and statistical analysis, and therefore the analysis they provide is not based on a complete, continuous record. Other instruments monitor every occurrence, but do not keep track of the sequence of events. That is, they measure every interval and keep track of how many times intervals of different lengths occur, but not the order in which they occur. A time-interval versus number-of-occurrences type of display only is provided, since time information has been lost in the process.
Until now, the instruments that made continuous measurements so that their output is based on a complete record, relied on post-processing to accomplish their analysis, and so their record length is always ultimately limited by memory size.
What is desired is a method and apparatus that performs time-interval to voltage conversion immediately and continuously, allowing timing variations to be viewed and correlated with other voltage signals displayed on an oscilloscope, and that preferably include means for producing a calibration output suitable for calibrating the vertical gain and offset of the oscilloscope, and that also preferably have means for automatically finding suitable resolution and offset settings that are appropriate to the signal and measurement being made.